This invention relates to a method for the interfacial polymerization of oligomeric chloroformates to product polycarbonates. The invention further relates to an efficient process for the continuous interfacial polymerization of oligomeric chloroformates to yield an aromatic polycarbonate.
Polycarbonates, prized for their transparency, toughness and relatively low cost, are produced globally on a scale of well over a billion pounds annually. Given the importance of polycarbonates in the fiercely competitive worldwide materials marketplace it is not surprising that new and more efficient routes to polycarbonates are earnestly sought. Numerous methods for polycarbonate preparation are well known, particularly for aromatic polycarbonates such as bisphenol A polycarbonate. Aromatic polycarbonates have been, and are currently prepared by two principal routes, the xe2x80x9cmeltxe2x80x9d method and the xe2x80x9cinterfacialxe2x80x9d method. The interfacial method is characterized typically by the reaction of a bisphenol with phosgene under interfacial conditions, that is, conditions generally comprising reaction in a water immiscible solvent such as methylene chloride in the presence of an aqueous solution of an acid acceptor such as an alkali metal hydroxide and a catalyst which is typically a tertiary amine such as triethylamine or a tertiary amine in combination with one or more phase transfer catalysts, such as tetrabutylammonium bromide.
One variation on the interfacial approach to polycarbonate preparation has been the bischloroformate method, sometimes referred to as the xe2x80x9cBCFxe2x80x9d method, in which the chloroformate groups of a low molecular weight oligomeric chloroformate are selectively hydrolyzed under conditions such that, when the chloroformate group is hydrolyzed thereby affording a negatively charged oxygen atom linked to the oligomer, the negatively charged oxygen atom reacts with one of the remaining chloroformate groups at a rate substantially faster that the rate at which the chloroformate groups are undergoing hydrolysis. The result of this rate differential is that the oligomeric chloroformate undergoes chain extension and polycarbonate having sufficient molecular weight to be useful is produced. While substantial research effort has been expended in the development of this xe2x80x9cBCFxe2x80x9d approach to polycarbonate and impressive achievements brought about, there remain opportunities for further improvement of this process. For example, it would be highly desirable to provide a method in which an oligomeric chloroformate could be continuously converted to high molecular weight product polycarbonate, and, without recourse to resubjecting the product to additional phosgene beyond that employed in the preparation of the oligomeric polycarbonate, afford a product polycarbonate which contained only very low levels of hydroxy groups, starting monomer and chainstopper. Frequently, however, the xe2x80x9cBCFxe2x80x9d approach affords a product polycarbonate which has an undesirably high level of hydroxy groups, contains high levels of residual monomer and chainstopper, and is generally unsuited for use in the continuous manufacture of polycarbonate. The present invention solves these and other problems which until now have long inhered to the xe2x80x9cBCFxe2x80x9d approach to polycarbonate manufacture.
In one aspect, the present invention provides a method of making an aromatic polycarbonate, said method comprising contacting under interfacial polymerization conditions a solution comprising an oligomeric chloroformate with an acid acceptor and a catalyst, said oligomeric chloroformate solution having a gross concentration of chloroformate groups, a total concentration of aromatic hydroxyl groups, and a net concentration of chloroformate groups, said net concentration of chloroformate groups being the difference between the gross concentration of chloroformate groups and the total concentration of aromatic hydroxyl groups, said net concentration of chloroformate groups having a value of greater than about 0.04 moles of chloroformate group per liter of said solution.
In another aspect, the present invention relates to polycarbonates prepared by the method of the present invention and articles comprising said polycarbonates.
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included herein. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
The singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise.
xe2x80x9cOptionalxe2x80x9d or xe2x80x9coptionallyxe2x80x9d means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
As used herein the term xe2x80x9cpolycarbonatexe2x80x9d refers to polycarbonates incorporating structural units derived from one or more dihydroxy aromatic compounds and includes copolycarbonates and polyester carbonates.
As used herein, the term xe2x80x9cmelt polycarbonatexe2x80x9d refers to a polycarbonate made by the transesterification of at least one diaryl carbonate with at least one dihydroxy aromatic compound.
xe2x80x9cBPAxe2x80x9d is herein defined as bisphenol A and is also known as 2,2-bis(4-hydroxyphenyl)propane, 4,4xe2x80x2-isopropylidenediphenol and p,p-BPA.
As used herein, the term xe2x80x9cbisphenol A polycarbonatexe2x80x9d refers to a polycarbonate in which essentially all of the repeat units comprise a bisphenol A residue.
As used herein, the term xe2x80x9cproduct polycarbonatexe2x80x9d refers to a polycarbonate product having a weight average molecular weights, Mw, greater than 15,000 daltons.
As used herein, xe2x80x9coligomericxe2x80x9d indicates a polymeric species having multiple repeat units and a weight average molecular weights, Mw, less than 15,000 daltons.
As used herein the term xe2x80x9cpercent endcapxe2x80x9d refers to the percentage of polycarbonate chain ends which are not hydroxyl groups. In the case of bisphenol A polycarbonate prepared from diphenyl carbonate and bisphenol A, a xe2x80x9cpercent endcapxe2x80x9d value of about 75% means that about seventy-five percent of all of the polycarbonate chain ends comprise phenoxy groups while about 25% of said chain ends comprise hydroxyl groups. The terms xe2x80x9cpercent endcapxe2x80x9d and xe2x80x9cpercent endcappingxe2x80x9d are used interchangeably.
As used herein, the terms xe2x80x9cchainstopperxe2x80x9d, xe2x80x9cchainstopping agentxe2x80x9d, xe2x80x9cendcapping agentxe2x80x9d and xe2x80x9cendcapxe2x80x9d have the same meaning and refer to a monofunctional species such as p-cumylphenol used to control the molecular weight of a product polycarbonate during the polymerization reaction in which the product polycarbonate is formed.
As used herein, the terms xe2x80x9chydroxy groupxe2x80x9d and xe2x80x9chydroxyl groupxe2x80x9d have the same meaning and refer to an OH group attached to an organic molecule which may have any molecular weight in a range between the molecular weight of methanol and that of the highest molecular weight polycarbonates achievable. Typically, as used herein, the terms refer to OH groups which are attached to the starting oligomeric chloroformate, or OH groups which are attached to the product polycarbonate.
As used herein the term xe2x80x9caromatic radicalxe2x80x9d refers to a radical having a valence of at least one and comprising at least one aromatic ring. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl. The term includes groups containing both aromatic and aliphatic components, for example a benzyl group, a phenethyl group or a naphthylmethyl group. The term also includes groups comprising both aromatic and cycloaliphatic groups for example 4-cyclopropylphenyl and 1,2,3,4-tetrahydronaphthalen-1-yl.
As used herein the term xe2x80x9caliphatic radicalxe2x80x9d refers to a radical having a valence of at least one and consisting of a linear or branched array of atoms which is not cyclic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of aliphatic radicals include methyl, methylene, ethyl, ethylene, hexyl, hexamethylene and the like.
As used herein the term xe2x80x9ccycloaliphatic radicalxe2x80x9d refers to a radical having a valance of at least one and comprising an array of atoms which is cyclic but which is not aromatic, and which does not further comprise an aromatic ring. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of cycloaliphatic radicals include cyclopropyl, cyclopentyl cyclohexyl, 2-cyclohexylethy-1-yl, tetrahydrofuranyl and the like.
The present invention relates to a method for preparing polycarbonate in which an oligomeric chloroformate in solution is reacted under interfacial conditions with an acid acceptor and a catalyst to form a high molecular weight polycarbonate. The oligomeric chloroformate comprises both hydroxyl end groups and chloroformate (CIOCO) end groups. It has been discovered that, surprisingly, when the concentrations of chloroformate and hydroxy endgroups present in a solution of an oligomeric chloroformate undergoing polymerization under interfacial conditions are suitably balanced, the product polycarbon ate possesses improved properties, such as containing a reduced amount of residual monomer and chainstopping agent. Additionally, the product polycarbonate so prepared contains a reduced level of hydroxy endgroups. By suitably balanced, it is meant that both the relative amounts of hydroxy and chloroformate groups and the actual concentrations of hydroxy and chloroformate groups in the solution undergoing polymerization are such that the xe2x80x9cnet concentrationxe2x80x9d of chloroformate groups present in the oligomeric chloroformate solution at the outset of the polymerization reaction is greater than about 0.04 moles of chloroformate groups per liter of solution. xe2x80x9cNet concentrationxe2x80x9d as used herein is defined as the difference between the total concentration of chloroformate groups (gross concentration) and the concentration of hydroxy groups present in the oligomeric chloroformate solution at the outset of the polymerization reaction. It is preferred that the net concentration of chloroformate groups be in a range between about 0.04 and about 1.2 moles of chloroformate groups per liter of solution. It should be emphasized that xe2x80x9cnet concentrationxe2x80x9d is based on the difference between the xe2x80x9cgross concentrationxe2x80x9d of chloroformate groups and the concentration of hydroxy groups present in the oligomeric chloroformate solution and that these concentrations are based upon the volume of the solution consisting essentially of the water immiscible solvent containing the oligomeric chloroformate at the outset of the reaction.
As noted, the polymerization is conducted under interfacial polymerization conditions, meaning the reaction mixture comprises water, at least one solvent which is not miscible with water, an acid acceptor, a catalyst, and the oligomeric chloroformate undergoing polymerization.
Suitable water-immiscible solvents which can be used under interfacial reaction conditions of the present invention are, for example, chlorinated aliphatic hydrocarbons, such as methylene chloride, carbon tetrachloride, dichloroethane, trichloroethane and tetrachloroethane; substituted aromatic hydrocarbons such as chlorobenzene, o-dichlorobenzene, and the various chlorotoluenes. The chlorinated aliphatic hydrocarbons, especially methylene chloride, are preferred.
Suitable acid acceptors include alkali metal or alkaline earth metal hydroxides which can be employed as acid acceptors under interfacial reaction conditions are, for example, lithium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide. Sodium and potassium hydroxides, and particularly sodium hydroxide are preferred.
The catalyst comprises one or more amine catalysts having structure I 
wherein R1-R3 are independently a bond, C1-C20 aliphatic radical, C4-C20 cycloalkylaliphatic radical, or a C4-C20 aromatic radical. Amines having structure I are illustrated by triethylamine, tributyl amine, N-butyl-N,N-dimethylamine, Hxc3x6nig""s Base, N-methylpiperidine, 4-(N,N-dimethylamino)pyridine, N-ethylmorpholine, 1,4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclco[4.3.0]non-5-ene, and the like.
The catalyst may further comprise a quaternary ammonium compound having structure II 
wherein R4-R7 are independently a bond, a C1-C20 aliphatic radical, C4-C20 cycloaliphatic radical , or a C4-C20 aromatic radical; and Xxe2x88x92 is an organic or inorganic anion. Typically the anion Xxe2x88x92 is selected from the group consisting of hydroxide, halide, carboxylate, phenoxide, sulfonate, sulfate, carbonate, and bicarbonate. Hydroxide is frequently preferred. Quaternary ammonium salts having structure II are illustrated by tetramethylammonium hydroxide, tetrabutylammonium hydroxide, and the like.
In an alternate embodiment of the present invention the catalyst further comprises a quaternary phosphonium compound having structure III 
wherein R8-R11 are independently a bond, a C1-C20 aliphatic radical, C4-20 cycloaliphatic radical , or a C4-C20 aromatic radical; and Xxe2x88x92 is an organic or inorganic anion. Typically the anion Xxe2x88x92 is selected from the group consisting of hydroxide, halide, carboxylate, phenoxide, sulfonate, sulfate, carbonate, and bicarbonate. Hydroxide is frequently preferred. Quaternary phosphonium salts having structure III are illustrated by tetrabutylphosphonium hydroxide, tetraoctylphosphonium hydroxide, tetrabutylphosphonium acetate, and the like.
In structures II and III, the anion Xxe2x88x92 is typically an anion selected from the group consisting of hydroxide, halide, carboxylate, phenoxide, sulfonate, sulfate, carbonate, and bicarbonate. With respect to catalysts comprising onium salts such as II and III, where Xxe2x88x92 is a polyvalent anion such as carbonate or sulfate it is understood that the positive and negative charges in structures II and III are properly balanced. For example, in tetrabutylphosphonium carbonate where R8-R11 in structure III are each butyl groups and Xxe2x88x92 represents a carbonate anion, it is understood that Xxe2x88x92 represents xc2xd (CO3xe2x88x922).
The oligomeric chloroformate used according to the method of the present invention may be an oligomeric chloroformate comprising either aromatic or aliphatic repeat units, or a combination thereof. Oligomeric chloroformates comprising aliphatic repeat units are exemplified by oligomeric chloroformates prepared from an aliphatic diols, for example, an oligomeric chloroformate having a degree of oligomerization of about 10 prepared from 1,6-hexanediol.
Oligomeric chloroformates comprising aromatic repeat units may be prepared from almost any dihyroxy aromatic compound either singly or as mixtures of dihydroxy aromatic compounds. Dihydroxy aromatic compounds are illustrated by bisphenols such as BPA and dihydroxybenzenes, for example resorcinol, hydroquinone, and methyl hydroquinone.
In one embodiment of the present invention the oligomeric chloroformate comprises repeat units having structure IV 
wherein R12 is independently at each occurrence a halogen atom, nitro group, cyano group, C1-C20 alkyl group, C4-C20 cycloalkyl group, or C6-C20 aryl group; n and m are independently integers 0-4; and W is a bond, an oxygen atom, a sulfur atom, a SO2 group, a C1-C20 aliphatic radical, a C6-C20 aromatic radical, a C6-C20 cycloaliphatic radical, or the group 
wherein R13 and R14 are independently a hydrogen atom, C1-C20 alkyl group, C4-C20 cycloalkyl group, or C4-C20 aryl group; or R2 and R3 together form a C4-C20 cycloaliphatic ring which is optionally substituted by one or more C1-C20 alkyl, C6-C20 aryl, C5-C12 aralkyl, C5-C20 cycloalkyl groups or a combination thereof.
Oliogomeric chloroformates comprising structural units IV are typically prepared from bisphenols such as bisphenols having structure V 
wherein R12, n, m, and W are defined as in structure IV.
Bisphenols having structure V are exemplified by bisphenol A; 2,2-bis(4-hydroxy-3-methylphenyl)propane; 2,2-bis(4-hydroxy-2-methylphenyl)propane; 2,2-bis(3-chloro-4-hydroxyphenyl)propane; 2,2-bis(3-bromo-4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-isopropylphenyl)propane; 1,1-bis(4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; 4,4xe2x80x2-dihydroxy- 1,1-biphenyl; 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dimethyl-1,1-biphenyl; 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dioctyl-1,1-biphenyl; 4,4xe2x80x2-dihydroxydiphenylether; 4,4xe2x80x2-dihydroxydiphenylthioether; 1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; 1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene; 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; and 1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene.
Typically, oligomeric chloroformates are prepared by reacting a bisphenol having structure V with excess phosgene under interfacial reaction conditions in which the pH is somewhat lower (pH from about 7 to about 9) than the pH typically employed in interfacial polymerization reactions of bisphenols with phosgene (pH between about 10 and about 12). U.S. Pat. Nos. 4,737,573 and 5,973,103 exemplify continuous and batch preparation of oligomeric chloroformate synthesis under pH-controlled and ratio-controlled caustic addition. Excess phosgene means an amount of phosgene which represents between about 3 and about 200 mole percent excess phosgene relative to the number of moles of bisphenol employed. It is frequently desirable to include a chain stopper during the preparation of the oligomeric chloroformate. Alternatively, the chain stopper may be added during polymerization of the oligomeric chloroformate. In some embodiments, a portion of the chain stopper may be added during the preparation of the oligomeric chloroformate and a second portion added during polymerization of the oligomeric chloroformate. In embodiments in which the chain stopper is added to the oligomeric chloroformate mixture it is advantageous to add said chainstopper only after the oligomeric chloroformate mixture is essentially phosgene-free, meaning that the organic solution contains less than about 10 ppm phosgene based on the weight of organic solution. The chain stopper is typically a monofunctional phenol such as p-cumylphenol. Monofunctional phenols having structure VI 
wherein R15 is a C1-C20 aliphatic radical, a C4-C20 aromatic radical, or a C3-C20 cycloaliphatic radical, and
s is an integer from 0-5, are suitable for use in the preparation of oligomeric chloroformates. The amount of chainstopper used typically corresponds to between about 0.1 and about 7 mole percent based on the number of moles of bisphenol used.
Suitable monofunctional phenols are exemplified by, but not limited to, the following: phenol; 4-phenylphenol, cardanol, eugenol, 4-t-butylphenol; p-cumylphenol; 3,5-dimethylphenol, and 2,4-dimethylphenol.
Although the method of the instant invention may be practiced in any suitable reaction vessel, such as a stirred tank reactor, or in any combination of reaction vessels in a batch or semi-batch process, the method is especially well suited for use in one or more continuous flow reactors. The flow reactor is not particularly limited and may be any reactor system which provides for the xe2x80x9cupstreamxe2x80x9d introduction of the reactants (oligomeric chloroformate and acid acceptor), catalyst, and solvent and water, and the xe2x80x9cdownstreamxe2x80x9d removal of product polycarbonate. Suitable flow reactor systems include tubular reactors, continuous stirred tank reactors (CSTRs), loop reactors, column reactors, and combinations thereof. The flow reactor may comprise a series of flow reactor components, as for example, a series of CSTRs arrayed such that the effluent from a first CSTR provides the input for a second CSTR and so forth. Combinations of the various flow reactor components are illustrated by a first CSTR coupled to a downstream column reactor where the output of the CSTR represents the feed to the column reactor. Additionally, the flow reactor used according to the method of the present invention may comprise flow reactor components arrayed in a parallel or network fashion, for example, as where the reactants are introduced into a single CSTR and the CSTR product is introduced into a parallel array of two or more tubular reactors. The advantage of this configuration is that multiple grades could be made simultaneously by, for example, introducing different proportions of chain stopper into the feed of each tubular reactor. In one embodiment of the present invention the flow reactor comprises a series of tubular reactors. In an alternate embodiment the flow reactor comprises a series of continuous stirred tank reactors. The reactants may be introduced into the flow reactor system through one or more feed inlets attached to the flow reactor system. Typically, it is preferred that the reactants, solvent and water be introduced into the flow reactor through at least two feed inlets, for example where a solution of the oligomeric chloroformate in an organic solvent such as methylene chloride and aqueous alkali metal hydroxide, and a solution of a catalyst in an organic solvent are introduced through separate feed inlets at or near the upstream end of a tubular reactor. Alternative arrangements wherein one or more of the reactants is introduced through multiple feed inlets at various points along the flow reactor are also possible. Typically, the relative amounts of the reactants present in the flow reactor are controlled by the rates at which they are introduced. For example, a reactant can be introduced into the flow reactor through pumps calibrated to deliver a particular number of moles of said reactant per unit time.
In one embodiment, the method of the present invention comprises the following steps:
Step (a) continuously introducing into a flow reactor a solution comprising an oligomeric chloroformate, said solution having a gross concentration of chloroformate groups, a total concentration of aromatic hydroxyl groups, and a net concentration of chloroformate groups, said net concentration of chloroformate groups being the difference between the gross concentration of chloroformate groups and the total concentration of aromatic hydroxyl groups, said net concentration of chloroformate groups having a value of greater than about 0.04 moles of chloroformate group per liter of said solution;
Step (b) continuously introducing into said flow reactor an acid acceptor and a catalyst; and
Step (c) continuously removing an effluent comprising and product aromatic polycarbonate.
In one embodiment said net concentration of chloroformate groups is in a range between about 0.04 and about 0.12 moles of chloroformate group per liter of said solution.
In one embodiment said flow reactor system comprises at least one tubular reactor, at least one continuous stirred tank reactor, at least one loop reactor, at least one column reactor, or a combination thereof.
In yet a further embodiment, the present invention provides a method of preparing bisphenol A polycarbonate, said method comprising
Step (a) continuously introducing into a flow reactor a methylene chloride solution comprising an oligomeric chloroformate, said solution having a gross concentration of chloroformate groups, a total concentration of aromatic hydroxyl groups, and a net concentration of chloroformate groups, said net concentration of chloroformate groups being the difference between the gross concentration of chloroformate groups and the total concentration of aromatic hydroxyl groups, said net concentration of chloroformate groups having a value between 0.04 and about 0.12 moles of chloroformate group per liter of said solution, said oligomeric chloroformate comprising repeat units having structure VII 
Step (b) continuously introducing into said flow reactor a solution of sodium hydroxide and water, and a solution of triethylamine catalyst in methylene chloride; and
Step (c) continuously removing an effluent comprising a product aromatic polycarbonate.
In one embodiment of the present invention no chainstopper is used in the preparation of the oligomeric chloroformate. However, chainstopper, an acid acceptor, a catalyst, and an essentially phosgene-free oligomeric chloroformate comprising repeat units IV are introduced into a flow polymerization reactor and continuously polymerized under interfacial conditions.